linux-kernel - [PATCH -V2 3/7] migrate_pages(): fix THP failure counting for -ENOMEM

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Date:   Mon, 11 Jul 2022 16:49:44 +0800
From:   Huang Ying <ying.huang@...el.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Huang Ying <ying.huang@...el.com>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        Zi Yan <ziy@...dia.com>, Yang Shi <shy828301@...il.com>
Subject: [PATCH -V2 3/7] migrate_pages(): fix THP failure counting for -ENOMEM

In unmap_and_move(), if the new THP cannot be allocated, -ENOMEM will
be returned, and migrate_pages() will try to split the THP unless
"reason" is MR_NUMA_MISPLACED (that is, nosplit == true).  But when
nosplit == true, the THP migration failure will not be counted.  This
is incorrect.  So in this patch, the THP migration failure will be
counted for -ENOMEM regardless of nosplit is true or false.  The
nr_failed counting isn't fixed because it's not used.  Added some
comments for it per Baolin's suggestion.

Signed-off-by: "Huang, Ying" <ying.huang@...el.com>
Fixes: 5984fabb6e82 ("mm: move_pages: report the number of non-attempted pages")
Reviewed-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
Cc: Zi Yan <ziy@...dia.com>
Cc: Yang Shi <shy828301@...il.com>
---
 mm/migrate.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 794312072eb3..38e2c789a9c3 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1426,11 +1426,11 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
 				/*
 				 * When memory is low, don't bother to try to migrate
 				 * other pages, just exit.
-				 * THP NUMA faulting doesn't split THP to retry.
 				 */
-				if (is_thp && !nosplit) {
+				if (is_thp) {
 					nr_thp_failed++;
-					if (!try_split_thp(page, &thp_split_pages)) {
+					/* THP NUMA faulting doesn't split THP to retry. */
+					if (!nosplit && !try_split_thp(page, &thp_split_pages)) {
 						nr_thp_split++;
 						goto retry;
 					}
@@ -1446,6 +1446,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
 				 * the caller otherwise the page refcnt will be leaked.
 				 */
 				list_splice_init(&thp_split_pages, from);
+				/* nr_failed isn't updated for not used */
 				nr_thp_failed += thp_retry;
 				goto out;
 			case -EAGAIN:
-- 
2.30.2